Patent Application
20240253192
This application claims priority to EP Patent Application No. 23154463.6, filed on Feb. 1, 2023, which is incorporated herein by reference in its entirety.
The present invention relates to a torque wrench for applying torque to fasteners. More specifically, the present invention relates to a digital torque wrench having a limit switch assembly configured to stabilize readouts displayed during operation.
Torque wrenches are well known in the art. Typically, a torque wrench includes a fastener drive structure having a fastener engaging head, such as a ratchet-type head, and an elongated tang member extending from the head. The fastener drive structure is inserted within a casing structure. The fastener drive structure and the casing structure are pivotally connected by a pivot pin for relative pivotal movement between a normal position and a torque exceeded position. A tang engaging member is biased by a spring into engagement with a rear end portion of the tang member to maintain the fastener drive structure and the casing structure in the normal position during a torque applying operation. An adjuster is provided to adjust the stress in the spring. During the application of torque to the fastener, the spring maintains the fastener drive structure and the casing structure in the normal position until the torsional resistance offered by the fastener reaches a threshold level determined by the spring force. Upon reaching that torsional resistance, the manual force being applied to the casing structure pivots the casing structure relative to the fastener drive structure, thereby causing the casing structure to contact the fastener drive structure to create an audible “click.” This “click” indicates to the user that the threshold level of torque has been reached.
Typically torque wrenches have been mechanical in nature. Recently, more and more wrenches are digital. Although they achieve a similar result as their mechanical counterparts, digital torque wrenches operate differently. One primary difference is the use of a loadcell. Within a digital torque wrench, loadcells may be a part of a loadcell assembly that also includes a loadcell holder, a wire and a printed circuit board assembly (PCBA). The wire of the loadcell assembly attaches the loadcell to the PCBA. As force is applied to the loadcell, it is converted into a change in electrical resistance that can then be measured. While digital torque wrenches may have some advantages such as accuracy; it also has some drawbacks. For example, during operation when the digital torque wrench clicks or breaks, additional extraneous forces may be applied to the loadcell. These forces may cause the reading of torque on the display to erroneously jump by as much as 10 percent. Thus, an operator seeking to torque a workpiece to 100 N-m may temporarily see a reading of as high as 110 N-m. Upon seeing such an erroneous reading, an operator may apply more (or less) torque to the workpiece than is necessary. The limit switch assembly of the present invention addresses this and other drawbacks.
The present invention is a limit switch assembly, which is defined according to the appended claims.
The accompanying drawings facilitate an understanding of the various embodiments of this invention. In such drawings:
The fastener drive structure 12 has a head 22 constructed and arranged to be removably engaged with a fastener and a tang structure 24 extending rearwardly from the head 22. The tang structure 24 has a hole 26 extending through a front portion 28 thereof. In the embodiment shown, the head 22 is a conventional socket-type ratchet head. The head 22 comprises a mounting portion 30 that is configured to engage the tang structure 24. The head 22 also contains a conventional ratchet drive assembly (not shown), which is received within the mounting portion 30. The ratchet drive assembly is well known in the art and need not be detailed herein.
The wrench body 14 includes a generally cylindrical casing structure 32 with generally cylindrical interior and exterior surfaces 34, 36. One end portion 38 of the casing structure 32 has a hole 40 therethrough. The opposite end portion 42 is constructed to mount the adjuster 20, described in greater detail below.
The fastener drive structure 12 and the casing structure 32 are pivotally connected for pivotal movement relative to one another about a pivot axis 44 between a normal position, as shown in
The tang engaging and stabilizing structure 16, includes a tilt block 48 and a pusher 50. The tilt block 48 includes a forward end 52 and a rearward end 54. As will be discussed below, when the casing structure 32 is in its normal position the forward end flushly engages a rear end portion 56 of the tang 24, and the rearward end 54, flushly engages the pusher 50. The term “flushly” simply means that a substantial portion of said end surface is in direct contact with its respective counterpart surface. Conversely, when the casing structure 32 is in its torque exceeded position, an edge 58 of the tilt block that is adjacent the forward end engages the rear end portion of the tang, and another edge 60 that is adjacent the rearward end engages the pusher.
The rear end portion 56 of the tang structure 24 and the pusher 50 each have a recess 62, 64 formed therein. Tilt block 48, is received in the recesses 62, 64 and is movable between the recesses 62, 64 to accommodate pivotal movement of the casing structure 32 and the tang engaging and stabilizing structure 16 relative to the fastener drive structure 12.
Those skilled in the art will recognize that the tilt block 48 may be a cube. Thus, forward and rearward ends 52, 54 of the tilt block 48 each have a pair of generally parallel edges 58, 60. The tilt block 48 and the recesses 62, 64 are oriented such that the pairs of generally parallel edges 58, 60 are arranged generally parallel to one another. Further, the tilt block 48 is configured such that a distance between opposite edges of the forward and rearward ends 52, 54 thereof is greater than a distance between adjacent edges of the forward and rearward ends 52, 54 thereof.
The stressed biasing element 18, in the form of a coil spring 66, applies a biasing force to the tang engaging and stabilizing member 16 to maintain the recess 64 of the pusher 50 in engagement with the tilt block 48 so as to maintain the casing structure 32 and the fastener drive structure 12 in the normal position thereof, as shown in
In the disclosed embodiment of the digital torque wrench 10, a loadcell assembly 76 is disposed between the cylinder 74 and the adjuster 20. The loadcell assembly 76 includes a loadcell 78, a wire 80, and a loadcell holder 82. The disclosed loadcell 76 is a strain gauge. However, those skilled in the art will recognize that other types of transducers that convert force into measurable output can also be used. The loadcell 78 may be substantially disc-like in shape and may include a protrusion 84 upon which compression or force can be directed. The cross-sectional area of the protrusion 84 is less than that of the overall area of the loadcell. Force applied to the protrusion 84 causes a slight deformation in the loadcell. The magnitude of this deformation can be measured and converted into a measurable output. When said force is released, the deformation goes back to its original position. A first end 86 of the wire 80 is connected to the loadcell 78. The second end 88 of the wire 80 is attached to a printed circuit board assembly (PCBA) 90, which for our purposes may also be considered to be a part of the loadcell assembly 76.
Those skilled in the art will recognize that the PCBA 90 is a circuit board that includes all the electrical components for the digital torque wrench soldered thereto. Among the components included as a part of the PCBA 90 are a display 92 for showing an information relating to the operation of the digital torque wrench 10. Also included is a micro-controller unit 94, which functionally acts as the brain of the PCBA 90. The PCBA 90 may also include a power switch 96, and a variety of connectors, including a battery connector 98 and a loadcell connector 100. As will be discussed below, the disclosed PCBA 90 also includes a limit switch assembly 102, which includes a limit switch housing 104 and an actuator 106. Those skilled in the art will recognize that the aforementioned list of PCBA components is not exhaustive.
The final component of the loadcell assembly 76 is the loadcell holder 82. The primary function of the loadcell holder 82 is to secure the loadcell 78 in a position wherein an accurate measure of the force applied thereto can be measured. To optimize this function, it is critical that both rotational and axial movement of the loadcell 78 be limited. The disclosed loadcell holder 82 achieves this. First, rotational movement of the loadcell 78 is limited by one or more (preferably two) prongs 108 that extend away from a load cell engagement surface 107 of the loadcell holder 82. These prongs 108 are configured to be received within mating recesses 110 on a loadcell holder engagement surface 109 of the loadcell 78. In an alternate embodiment (not shown), the prongs can be on the loadcell, and the mating recesses can be in the loadcell holder. In yet another embodiment (also not shown), one prong and one mating recess can be in each of the loadcell and the loadcell holder. Irrespective of the embodiment, what is important is that the loadcell 78 and the loadcell holder 82 are connected to one another such that if any inadvertent rotational movement is applied, neither the loadcell nor the loadcell holder will rotate independent of one another.
In addition to limiting rotational movement of the loadcell, the loadcell holder also limits its axial movement. This is achieved with the use of a detent or a rounded surface. As best seen in
As best seen in
With the loadcell 78 positioned within the casing structure 32 and the PCBA positioned outside the casing structure 32, the loadcell wire 80 must run from inside the casing structure 32 on one end 86 to the PCBA 90 (outside the casing structure 32) on the other end 88. Having the wire 80 both inside and outside the casing structure 32 can lead to tangling problems during operation of the digital torque wrench 10. To manage the wire 80, a wire holder 128 is utilized. The wire holder 128 includes a body 130 having a neck 132 and a first arm 134 and second arm 136 that form a clip 138, wherein said clip 138 is configured to secure the body to a casing structure 32 within the digital torque wrench 10. The wire holder 128 further includes a groove 140 formed between first and second walls 142, 144 that run down neck 132 and one of either the first or second arms 134, 136, and wherein said groove 140 is configured to receive the wire from the loadcell assembly and facilitate the coiling of said wire about the casing structure 32 above the clip 138 as the wire holder 128 translates up and down the casing structure 32. To facilitate said translation, the neck 132 may further include one or more protrusions 146 that extend away from the first and second walls 142, 144, wherein said protrusions 146 are configured to extend into a slot 148 of the casing structure 32 and engage an element of the digital torque wrench 10 that translates in response to the rotational movement of the adjusting shaft 150. More specifically, the protrusions 146 may engage a part of the loadcell assembly 76. Even more specifically, the protrusions 146 may engage a wire holder engagement portion 152 on the loadcell holder 82. The wire holder engagement portion 152 may be a shelf-like structure on a side of the loadcell holder 82. More specifically, the wire holder engagement portion 152 may be positioned in one or more grooves 115 in the loadcell holder. These grooves 115 also receive and guide the wire 80 of the loadcell 78. To facilitate engagement, the protrusions 146 may be positioned so that there is at least one upper protrusion 146a and at least one lower protrusion 146b. In a preferred embodiment, the space between the upper protrusion 146a and lower protrusion 146b is sized to respectively engage an upper and lower surface 152a, 152b of the wire holder engagement portion 152.
The PCBA 90 of the digital torque wrench 10 also includes a limit switch assembly 102. The limit switch assembly 102 is configured to stabilize the readout on the display during operation. The limit switch assembly 102 includes a housing 104, and an actuator 106 partially disposed therein. The actuator 106 includes a switch end (not shown) that is disposed within the housing 104, and an engagement end 154 is positioned outside of the housing 104. The actuator is configured to be movable between a first position, wherein the engagement end 154 is distal from the housing 104 (see
The limit switch assembly 102 is positioned on the PCBA 90 such that the actuator 106 can be moved between its first and second positions with the handle assembly 156. The handle assembly 156, which is a part of the adjuster 20, includes a handle 158 and a locking ring 160 that is biased by a spring 162. The locking ring 160 is configured to prevent unwanted rotational movement in the handle 158. The locking ring 160 is movable between a first and second position. In the first position, the locking ring limits rotation of the handle 158. In the second position, the locking ring permits rotation of the handle 158. Thus, when the locking ring is in its second position, inadvertent adjusting of the digital torque wrench 10 is avoided. In operation, a user may pull the locking ring 160 against the bias of the spring 162 toward its second position. This unlocks the handle and permits rotational movement of the handle 158. When the user releases the locking ring 160, the spring biases the locking ring back into its first position where rotational movement of the handle is limited. The locking ring 160, also includes a limit switch engaging surface 164. The spring 162 biases the locking ring, and more specifically, the limit switch engaging surface 164 into contact with the limit switch actuator 106. The force of the spring 162 is greater than that of the biasing element that biases the actuator towards its first position. Thus, in the absence of any external forces, the actuator 106 is held in its second position.
The operation of the digital torque wrench 10 will now be described in greater detail. The first step is to adjust the digital torque wrench to the desired torque level setting. For example, if an operator wishes to set the digital torque wrench to 100 N-m she will pull down the locking ring 160 and rotate the handle 158. Rotation of the handle 158 causes a series of interconnected elements to advance (or retract) against the biasing element 18. Those skilled in the art will recognize that the biasing element 18 may be a coil spring 66. As best seen in
The rotation of the handle 158 will cause the cylinder 72, loadcell assembly 76 and spacer 74 to advance against the coil spring 66. This advancement will impart force onto the protrusion 84 of the loadcell 78 within the loadcell assembly 76. Force applied to the protrusion 84 causes a slight deformation in the loadcell 76. The magnitude of this deformation can be measured and converted into a measurable signal. This signal is transferred from the loadcell 76 to the PCBA 90 via wire 80. The micro-controller 94 of the PCBA 90 converts the signal into N-m, in our example, 100 N-m, which is displayed on the display 92. Once the desired torque level is achieved, the operator may release the locking ring 160. The digital torque wrench can then be used to apply torque to a workpiece.
Except for the PCBA 90 and the wire 80, each of the aforementioned interconnected elements are disposed within the casing structure 32. The PCBA is outside of the casing structure 32, and the wire 80 runs between the PCBA 90 to the loadcell 78 via slot 148. The various rotation and translation of interconnected elements can cause the wire 80 to become tangled and/or pinched between moving parts. To manage the wire 80, a wire holder 128 is utilized. The first and second arms 134, 136 of the wire holder form a clip 138 that is configured to secure the wire holder 128 to the casing structure 32. The groove 140 of the wire holder is configured to receive the wire from the loadcell assembly and facilitate the coiling of said wire about the casing structure 32 above the clip 138 as the wire holder 128 translates up and down the casing structure 32.
As the interconnected elements are translated and force is applied to the loadcell 78, it is critical that both rotational and axial movement of the loadcell 78 be limited to obtain accurate loadcell measurements/readings. The loadcell holder limits rotational movement with prongs 108 that extend away from its surface and are disposed within mating recesses 110 on an adjacent surface of the loadcell 78. The loadcell holder 82 limits axial movement with a detent 114 that is disposed in a convex recess 112 in a surface of the loadcell holder 82 such that a portion of the detent extends away from said surface. The detent limits axial movement of the loadcell by automatically aligning it with the loadcell holder and any force applied thereto.
Going back to our example, after the digital torque wrench 10 is adjusted to 100 N-m, the operator may begin to apply torque to a work piece. Those skilled in the art will recognize that when 100 N-m of torque is reached, the tilt block 48 will partially rotate between the pusher 50 and tang 24. This rotation will cause the familiar break or “click” that informs the operator that she has reached the desired torque level. Prior to the present invention, digital torque wrenches that utilize a loadcell may experience an unwanted jump in torque measurement that led to a temporary display reading 110 N-m or more. This inaccurate temporary reading is due to the extraneous forces that are applied when the torque wrench breaks. These forces may include vibrations of the casing structure, shear forces from the tilt block, friction forces, etc. Eventually these forces dissipate and the reading on the display may go back to the desired level. However, by then it may be too late as the operator may have already applied (or removed) torque to reach what she understood to reach her desired level.
The digital torque wrench 10 of the present invention avoids these inaccurate readings by always preventing these inaccurate temporary jumps in display readings. This is achieved through the use of the limit switch assembly 102. The limit switch assembly 102 is configured to stabilize the readout on the display during operation of the torque wrench.
When an operator pulls down the locking ring 160 to begin adjustment to the desired torque level, she disengages the limit switch engaging surface 164 from the actuator 106 of the limit switch assembly 102. A biasing element within the limit switch housing 104 moves the actuator 106 towards its first position, wherein the engagement end 154 of the actuator 106 is distal from the limit switch housing 104. When the actuator 106 is in this first position, the micro-controller 94 will continually read the force measurement signals received from the loadcell 78, convert them to torque, and display the real-time torque. The torque wrench may then be adjusted to the desired level, for example, 100 N-m. The operator may then release the locking ring 160. Spring 162 moves the locking ring 160 back toward its first position such that the limit switch engaging surface 164 thereof contacts the actuator 106 and pushes it back into the limit switch housing 104. This is the second position of the actuator 106. When the actuator 106 is moved to its second position, the micro-controller 94 marks the last received force measurement from when the actuator 106 was in the first position as Fset and displays the corresponding torque as Tset. In our example, the micro-controller 94 records the last received force measurement as Fset and converts it to the corresponding torque Tset, or 100 N-m. All subsequent force signals received from the loadcell 78 will be converted torque and compared to Tset.
The operator then uses the digital torque wrench 10 to apply torque to the work piece. During this process, force is applied to the loadcell 78. These forces are marked by the micro-controller 94 as F1, converted to torque T1 and then compared to Tset. If T1 is less than Tset or within a predetermined range thereof, the micro-controller 94 will display the corresponding torque measurement T1. Alternatively, if T1 is greater than Tset and outside the predetermined range, the micro-controller 94 will display Tset. Those skilled in the art will recognize that the predetermined range is dependent on the digital torque wrench's desired level of accuracy, and thus may be any percentage (plus or minus) of Tset. For example, the predetermined range may be 4%.
Going back to our example, as the operator uses the digital torque wrench, varying levels of force are applied to the loadcell. At any given time, the micro-controller reads this force as F1, converts it to its corresponding torque T1, compares it to Tset and then displays a value according to rules set forth in the previous paragraph. In our example, where Tset is 100 N-m and the predetermined range is 4%, exemplary values may be as those set forth in the following table:
As can be seen, in those instances where the real time converted torque T1 is less than Tset or within the predetermined range (plus or minus 4%) thereof, the micro-controller displays the real time converted torque T1. However, in those instances wherein the real time converted torque T1 is both greater than Tset and outside of the 4% range, the micro-controller displays a value of Tset. This prevents a display of an unwanted real time converted torque value T1 caused by jump in reading due to the “click” and extraneous forces.
When an operator is using the digital torque wrench, force will eventually be applied to the loadcell having a converted real time torque T1 that approaches Tset. As greater and greater torque is applied, the value eventually reaches 100 N-m and the digital torque wrench breaks or clicks. At this moment, the extraneous forces may be applied to the loadcell 78. These extraneous forces may have a converted real time torque T1 of 110 N-m. Displaying this erroneously high T1 is to be avoided. Thus, the micro-controller of the present invention, recognizes that the limit switch actuator is in its second position and thus displays real time converted torque values according to the aforementioned rules. Thus, the value of Tset (100 N-m) will be displayed.
Following the break, the extraneous forces dissipate. To be sure that the wrench has torqued the workpiece to the desired level, the micro-controller 94 may, after a predetermined amount of time, take another force measurement F2, convert that to a real time torque T2 and compare that to Tset. Said predetermined amount of time may be, for example, 2 seconds. If T2 is greater than Tset and outside a predetermined range away from Tset, the micro controller will display a visual indicia indicating the torque is greater than Tset. For example, the micro-controller might display the word, “HI” or another indication that the torque is greater than Tset. Alternatively, if T2 is less than Tset and outside a predetermined range away from Tset, the micro-controller will display a visual indicia indicating the torque is less than Tset. Thus, the micro-controller might display the word, “LO” or another indication that the torque is less than Tset. Finally, if T2 is within the predetermined range of Tset, the micro-controller 94 will display Tset.
This final display of Tset will be in the operator's indication that she has reached the desired torque level and that she should stop applying torque. In order to confirm the same, the micro-controller may provide a secondary indication of having reached the desired level. Said secondary indication may be visual, such as a flashing display of the Tset value. The secondary indication may be audible, such as a beep. The secondary indication may also be tactile, such as a vibratory response. Those skilled in the art will recognize that the secondary indication may also be a combination of the visual, audible or tactile responses.
It can thus be appreciated that the various objectives of the present invention have been fully and effectively accomplished. The foregoing specific embodiments have been provided to illustrate the structural and functional principles of the present invention and is not intended to be limiting. To the contrary, the present invention is intended to encompass all modifications, alterations, and substitutions within the spirit and scope of the appended claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23154463.6 | Feb 2023 | EP | regional |
